1. Field of the Disclosure
The present disclosure relates to the field of optical absorption laser spectroscopy. More particularly, the present disclosure relates to a method and apparatus for increased purge efficacy in optical absorption spectroscopic measurements of gases in sealed containers.
2. Background Information
There presently exist systems in which gases in volume product containers are detected, analyzed and/or measured during pharmaceutical, food and beverage, consumer electronic production and the like. Optical absorption laser spectroscopy can quantify the amount of matter in a sample by directing laser energy at a sample of matter and measuring how much laser intensity is absorbed. Such systems can measure trace quantities and can nondestructively analyze gas contents within sealed containers, in order to determine, e.g., the amount of contaminants/species present in a sealed container.
FIG. 1 shows a related art optical absorption laser spectroscopy system 10 found in, e.g., U.S. Pat. No. 7,067,323, the contents of which are expressly incorporated herein in their entirety. Such a system 10 generally contains a light source 42, a container 14, a light collection element 44, and a light detector 48, and can be an enclosed design.
The region between the light source 42 and the light detector 48 is typically referred to as a sample region or detection zone 26. In other words, in the detection zone 26, the light emitted from the light source 42 passes through the detection zone along the optical axis of the light source and onto the detector. The light is of a special variety that is absorbed by a spectroscopic species of interest in a way that is detectable, which is considered the signal to be detected. The light collection is usually done with an optical lens 44. The optical path B includes the light rays that are emitted by the laser light source 42 and also sensed by the detector 48. Absorbers that are outside of the container 14 yet within the optical path B can adversely affect the signal picked up by the detector 48 as well as absorbers that are inside. To reduce or eliminate the effect of these external absorbers, some other inert gas (that does not contain absorbers, such as nitrogen) can be pumped into the optical path B from a gas source by a purging system 54 to displace or remove the ambient gas from the top of the detection zone 26, which is referred to as a purge. By purging the unwanted gas or air through passages 56, the system 10 can better determine solely the concentration of absorbers within a container, and to a high degree of accuracy.
For example, when detecting oxygen in a sealed pharmaceutical sample container, the oxygen in the atmosphere outside the container but along the laser path must be removed. Purging this gas away from the sample container is often the quickest and most efficient method for removing interfering gas species from the measurement region.
Optical absorption laser spectroscopy using sealed containers 14 that move quickly through the detection zone 26 can be a challenge due to the entrained flow of such as ambient air. A closed system where a purge gas can reliably displace all ambient gas and where the container to be measured is inserted into the apparatus can be forgiving with respect to the particular flow of the purge, so long as it is good enough to remove most of the ambient gas eventually, as the physical limitations of it are such that measurements take tens of seconds to minutes.
FIG. 2 shows a laser module of a related art optical absorption laser spectroscopy system. In this example, the laser source 42 is present in laser source housing 58a, and includes a pair of passages 56 in the form of purge holes on opposite sides of the laser source. The flow of purge gas must be high in order to discharge and fill up the detection zone 26 with purge gas in a timely manner. Other related art laser modules have a plurality of purge holes that encircle the laser source 42. The purge hole pattern determines the fluid flow dynamics when the purge gas flows out of the detector housing 58b and into the detection zone 26. Generally the purge hole pattern encircling the laser source 42 requires a large volume of purge gas, and does not rapidly fill the volume outside the detector (i.e., the detection zone 26) with the purge gas, thereby slowing down the detection process.
In view of the above, a need has arisen to economically and rapidly purge gas from a detection zone during optical absorption spectroscopic measurement of gases in sealed containers.